Tempers flared yesterday at six-party talks on the North Korean nuclear crisis, with negotiators clashing as they strove to draw up a joint statement of principles that has eluded them for nearly three years.

No one believed the document would contain ground-breaking commitments, but even outlining the basics was proving elusive.

One Japanese delegate said yesterday's meetings had been "frank and constructive", adding: "Depending on the issues, there were scenes of fierce exchanges."

Discussions on the draft were set to drag on into today, the seventh day of talks in Beijing. South Korean envoy Song Min-soon said that so far the six delegations had agreed only to establish a framework for denuclearisation of the Korean Peninsula.

Despite an unprecedented flurry of one-to-one meetings, the main protagonists, Washington and Pyongyang, still appeared far apart on the critical issue of how and when the North's nuclear weapons programmes should be dismantled.

Chief negotiators from the two Koreas, China, the US, Russia and Japan had left their deputies to haggle over the text of the draft statement put forward by China, with the aim of producing a joint document that all parties could sign.

US chief negotiator Christopher Hill told reporters: "It's a very lengthy, difficult process."

The Chinese draft paper calls on Pyongyang to abandon its "nuclear weapons programme and related programmes", a diplomatic source close to the talks said.

In return, the paper calls on the other five countries to provide "security guarantees" and economic aid and to normalise or improve ties with Pyongyang, the source said.

But the draft does not say who should move first or if the parties should move simultaneously, avoiding the issue of timing that is the essence of Pyongyang's disagreement with Washington.

Having any statement at all agreed by the six parties would mark a breakthrough for the Beijing talks, where past progress has been measured by whether they could agree even to reconvene. This round, the fourth since the crisis erupted in 2002, is open-ended.